Metal catalysts, usually in elemental or organometallic form but sometimes in lower valency form, particularly Group VIA and Group VIII metals, are widely used for a variety of catalytic procedures involving unsaturated compounds, such as hydrocarbons, including hydrogenation, oxidation, carbonylation, hydroformylation, hydration, solvolysis, isomerization and dimerization.
Generally, however, such metal catalysts are difficult to handle and use effectively and present difficulties in achieving economic separation of the used catalyst for reuse, especially when in the form of a soluble metal complex.
Catalysts have been suggested wherein covalent bonding exists between an active metal complex and an insoluble polymer. This procedure often causes a decrease in the activity of the catalyst, which may be a result of the functional groups of the polymer occupying coordination sites of the metal complex. For metal complexes to possess high activity, some degree of coordinative unsaturation must exist, or be easily achieved, in order that substrate activation can occur. Covalent attachment of the complex to a polymer support may limit the degree of coordinative unsaturation appreciably. For example, it has been reported by Z. M. Michalska and D. E. Webster, Platinum Metals Rev., 18, 65 (1974) that the activity of rhodium catalysts covalently attached to polystyrene are only 0.06 times that of an equivalent amount of the homogeneous counterpart.
Furthermore, introduction of the desired functionality to a polymer, that will enable it to covalently bind a catalyst may also cause undesirable functionality to be introduced. The undesired functionality, caused by a side reaction, may depress catalyst activity.